1. Field of the Invention
The present invention relates to ammunition articles including casing and projectile components that are sealed against penetration of moisture, e.g., atmospheric water vapor, into the seam between the casing and projectile and the interior compartment of the casing. The invention further relates to a method of manufacturing such ammunition articles, for high-volume production of such ammunition articles.
2. Description of the Related Art
In the field of munitions manufacturing, processes have been developed for high-volume production of ammunition articles including casing and projectile (bullet) components that are assembled into the final product article, with gunpowder or other explosive medium, and optionally a primer, in the interior volume of the casing.
A recurrent problem with such ammunition articles is their susceptibility to incursion of moisture, such as ambient atmosphere water vapor, at the seam between the casing and projectile components. Any such ingress of moisture is detrimental to the operation and reliability of the ammunition article, and can compromise the safety of the ammunition user.
In the manufacture of ammunition, the bullet or projectile is inserted into the open end of the casing that contains the powder charge and primer. Though the projectile is designed to fit tightly into the opening, a small gap remains at the interface between the casing and the bullet, which is susceptible to ingress of moisture, as described.
Since ammunition may be stored for long periods of time before use in a wide variety of environments, including marine and aquatic environments, and in adverse weather environments involving rain, snow or even high relative humidity conditions, a technique is required to seal the casing/projectile interface of the ammunition article at the time of its manufacture, so that the ammunition article thereafter is safeguarded against adverse moisture-containing environments that may otherwise effect moisture permeation into the interior of the casing.
The traditional technique for sealing small-caliber ammunition has been application of an asphalt-based sealant applied to the inside of the mouth of the casing before the bullet is inserted. This technique is unsatisfactory for many reasons. First, as the bullet is inserted into the casing after the application of the sealant, much of the sealant is pushed downwardly into the casing, thereby removing it from any sealing ability, so that there is a wastage of the sealant material. Second, because of the displacement of the sealant into the casing compartment by the bullet, the gap between the bullet and the casing in many instances is not fully sealed around the full circumference of the bullet at the interface with the casing, and the aforementioned moisture permeation problems remain. Third, the sealant, as an inert mass that is displaced into the portion of the casing holding the powder charge, will agglomerate the powder it contacts, thereby interfering with the desired homogeneous character and firing of the powder charge. Fourth, as the charge is ignited in subsequent use of the ammunition article, much of the sealant does not ignite and is deposited in the weapon during firing. The resulting residue interferes with the subsequent operation of the weapon using such ammunition and complicates the cleaning and maintenance of the weapon after its use. Fifth, the chlorinated solvent in which the asphalt-based sealant is dissolved has been determined to be harmful to the environment. For all these reasons, the traditional asphalt-based sealant approach is highly deficient in producing a safe, effective, and reliable moisture seal at the projectile/casing interface.
One approach designed to overcome the environmental problem is to replace the chlorinated solvent with water. This water-based sealant approach also suffers the aforementioned deficiency that much of the sealant applied to the inside of the case is pushed down into the case as the bullet is inserted during assembly, and the remaining sealant produces an irregular (and often incomplete) seal, which results in a large number of assembled ammunition articles being rejected. It also suffers the deficiency that the water-based sealant that is pushed down into the casing is mixed with the powder charge. Subsequently, when the ammunition is fired, the sealant is not entirely consumed as the powder ignites. The sealant residue is expelled into the chamber and barrel of the weapon, requiring additional cleaning of the weapon and possibly affecting the weapon's subsequent functioning. Finally, the water-based sealants used in this approach require up to 20 seconds to set, thus involving an extended processing time that is inconsistent with high-speed munitions manufacturing processes.
U.S. Pat. No. 6,367,386 issued Apr. 9, 2002 and U.S. Pat. No. 6,584,909 issued Jul. 1, 2003 disclose a method in which a capillary-active, acrylate-based anaerobic adhesive sealing agent is applied to the gap of the fully manufactured cartridge. This method is unsatisfactory for various reasons, including the fact that anaerobic adhesives behave inconsistently. They can solidify during application, resulting in the total loss of costly processing equipment. Due to differences in manufacturing equipment, processing speeds, process temperature conditions and metals, gaps between cartridges and projectiles are rarely identical. As a result of this structural variation, anaerobic adhesives do not seal with a uniform degree of adhesion. Occasionally the bond of the projectile to the cartridge is too strong, causing the weapon to explode. When relatively large gaps occur the presence of oxygen can prevent the cure of the anaerobic adhesive, resulting in an unprotected cartridge.
The foregoing discussion reflects the failure of the art to satisfactorily address and resolve the problem of sealing ammunition articles at the interface of the casing and projectile, in a manner that is amenable to high-speed manufacturing of ammunition articles, to produce consistent and reliable sealing of the casing/projectile seam, without the problems incident to prior art approaches that compromise the integrity and function of the powder charge in the cartridge, and introduce substantial weapons cleaning and maintenance issues.
It would therefore be a significant advance in the art to provide an ammunition article and manufacturing method that overcome the aforementioned deficiencies of the prior art.